Skip to main content
Commercial superphosphates contain 14-20% of PaO6 soluble in water and
citrate; their strength, in percentage of PaO0, is only guaranteed as 14/16,
15/17, 16/18, 18/20. The normal percentage of moisture is 10-15 m mineral
superphosphates and 13-16 in those from bones.
Bone superphosphates contain i-i'5% of organic nitrogen and are to be
regarded as genuine when they contain less than <>M% AUG., + Fe2OB, less
than 0-1% CaFjj, less than 0-05% CaCla, less than i% SUX, less than 0-3% of
residue insoluble in acids, (and this is free from nitrogen) ami no manganese, and
when the value of the ratio CaO : P2()fi lies between 1-30 ami 1-35, that: of SO3
X 100 : total PaOr, is 110-129, and that of SO., X 100 : soluble! Pa(.')G 110-132
(in the last two ratios SO., and P,jOn are referred to 100 parts of dry sub-
The mineral superphosphates, on the other hand, contain no nitrogen, but
relatively large proportions of alumina and ferric, oxide, fluorine, silica and
insoluble residue ; further the ratio SO,, x 100 : total Pa<'>r, iHi -227 and SO,,
X 100 ; soluble PaOr, ~~ 184--242 (SO., and PaO5 reCerred to dry substance).
Double and triple supc.rphosph.alcs contain 40--45% P./V
Dcphosphorisation slag, or Thomas xltig, forms a. line, brownish-grey
powder, and it. contains calcium phosphate, mostly (75 70% of the total
PaOB) soluble in ammonium citrate or eitrie acid, and on this its value depends.
Analysis of this product comprises the following :
1. Total Phosphoric Anhydride (L<w's method}. 5 grains of sub-
stance, placed in a 250 c.c. measuring lla.sk, arc moistened with water, 25-
30 c.c. of cone, sulphuric; acid added, and the llask, covered with a funnel,
heated on a gauze or sand-bath until white vapours are emitted ; (he liquid
is then diluted with water, allowed to cool, ma.de up to volume with water
and mixed. To 50 c.c. of the filtered liquid ( i gram of substance) are
added 20 c.c, of ammonium citrate, 50 c.c. of water, 50 e.c. of ammonia
(1) -- 0-92), and 50 c.c. of magnesia, mixture, the procedure (lien being that
for the ordinary determination of total phosphoric anhydiide \scc General
2. Phosphoric Anhydride soluble In Citric Acid (\Vtinner's method}.
-......-The following solutions are required :
(a) Citric Acid. 100 grams of the crystallised acid and 0-05 grain of
salicylic acid are dissolved in water to I litre. Immediately before use, I
vol; of this solution is diluted with 4 vols. of water, this giving the 2% citric
acid solution necessary for the determination.
(b) Molylidic solution. 150 grams of pure ammonium molybdate are
dissolved in 500 c.c. of water and the solution poured into i litre of nitric
acid (!) rig), 400 grams of ammonium nitrate being added, the volume
made up to 2 litres with water, the liquid left at about 35" for 24 hours and
(c) Magnesia, mixture. This is prepared as indicated on p. 123.
MODE OF WORKING :
5 grams of slag, in a graduated 500 c.c. flask, are moistened with
5 c.c. of alcohol and the volume made up, gradually and with thorough-
shaking, with the 2% citric acid solution. It is then rotated mechanicallyital., 1898, p. 270) ; F. Martinotti: "A Method for Distinguishing Bone Phog